Turbocharger Design & Analysis Solutions. Bill Holmes Brad Hutchinson Detroit, October 2012

Transcription

1 Turbocharger Design & Analysis Solutions Bill Holmes Brad Hutchinson Detroit, October 2012

2 Agenda ANSYS overview ANSYS TurboSystem Blade row solutions The ANSYS Transformation methods An example: turbocharger compressor analysis Summary

3 ANSYS Vision for Rotating Machinery: Full machine simulation High fidelity simulation of all components Simulate complex phenomena and processes Unsteady combustion, compressor stall, cavitation, noise, fracture, component interactions, advanced materials... Integrated tool set for all geometry and physics Large scale High Performance Computing (HPC) enabled

4 ANSYS TurboSystem

5 ANSYS Axial and centrifugal compressors Axial and radial turbines (Steam & gas) Centrifugal, mixed flow and axial pumps Axial and radial fans Automotive turbomachinery Water turbines Wind turbines

6 ANSYS TurboSystem Complete turbomachinery design and analysis in ANSYS Workbench Geometry Throughflow Meshing CFD Thermal Combustion Structural mechanics Rotordynamics Post processing Optimization This presentation will focus on ANSYS blade row fluid dynamics for turbocharger compressors

7 ANSYS Workbench Parametric Geometry (Meanline & Through-Flow) Mesh Robust Design Analysis

8 ANSYS Workbench

9 ANSYS Workbench

10 ANSYS Workbench

11 ANSYS Workbench

12 ANSYS Workbench

13 ANSYS Workbench

14 ANSYS Workbench

15 ANSYS Workbench

16 ANSYS Workbench

17 ANSYS Workbench

18 BladeModeler Meanline Design Vista CCD Centrifugal compressor rotor design Real gas capability

19 BladeModeler Meanline Design Vista RTD Radial turbine preliminary design

20 ANSYS BladeModeler Design comparison Visible in meridional sketches, angle/thickness views, blade to blade view and 3D view

21 ANSYS TurboGrid Automated grid generation for bladed turbomachinery components High quality hexahedral grids Repeatable Minimize mesh influence in design comparison Scalable Maintain quality with mesh refinement

22 Centrifugal Compressor

23 ANSYS Turbomachinery Fast & scalable solver Low speed to supersonic Steady/transient Turbo specific BC s Turbulence & heat transfer Multiple Frame of Reference Multi phase flow Real fluids Fluid/structure interaction

24 Turbulence Model Detached Eddy Simulation Laminarturbulent transition Streamline curvature & rotation Scale Adaptive Simulation SST Model 'Automatic' wall functions Wall roughness Stagnation line flows EARSM

25 ANSYS Design Exploration Sensitivity analysis Design optimization Robustness evaluation initial

26 Mechanical Mechanical deformation Rotational forces Surface pressure loads Thermal stress Temperature, Heat flux, Modal analysis Frequencies Blade flutter Aerodynamic damping Forced response Transient Rotor Stator Full 2 way FSI

27 ANSYS Transient Blade Row Methods

28 TBR with pitch change: The ANSYS Transformation methods Problem: How to obtain the full wheel transient solution, but at low cost? Solution: The ANSYS TBR Transformation family of methods onew models minimize number of simulated passages, providing enormous efficiency gains and reduced infrastructure requirements

29 Steady with Pitch Change Fast Blade Row Solutions Transient with Pitch Change Transient Full-Domain Time Domain Profile Transformation Time Transformation Status: Release & Beta Fourier Transformation Frequency Domain Harmonic Transformation Status: Development

30 ANSYS TBR Applications Single Stage Multi Stage Gust Analysis Turbine TBR Applications Blade Flutter displacement Period Gust speed Blade Passage pitch 2 IBPA j Nb j 0 Nb 1 Damping Coef. IBPA Gust pitch

31 Turbocharging Unsteady State Rotor Stator Interaction (Off Design) Inlet distortion Acoustics Turbulent flow with conjugate heat transfer Multi physics Forced response Thermal Optimization & Robust Design Map Width Enhancement, mixed flow turbine wheels, volute configuration ETH Zurich

32 Multi Physics Modeling 3D CAD CSM Mesh CFD Mesh Load Transfer Static & Thermal CSM Aerodynamic CFD

33 ANSYS Turbo System Geometry Mesh Analysis CAD Throughflow Robust Design ANSYS Workbench

34 Example Application: Turbocharger Compressor

35 Turbocharger Compressor Analysis: A Best Practice Example Methodology Preliminary Design Geometry & Meshing Impeller only analysis Impeller diffuservolute analysis Post processing and interpretation

36 Methodology Pre CFD Start with geometry that meets design specifications From Vista CCD, CCM, TF and BladeModeler Impeller only analysis The impeller is the heart of the compression system understand it first Overall performance: how good can it be, can it be better? Nature of the flow, strengths and weaknesses What factors affect performance? Predictions? Whole system Impeller diffuser volute analysis Volute only analysis useful? Post processing Quantitative and qualitative

37 Geometry 1 D design developed in VISTA CCD Based on prescribed duty, design constraints Impeller Geometry VISTA CCD, CCM BladeModeler VISTA TF Make adjustments according to package constraints, design rules, approach etc. Meridional path Blade profile/thickness Hub/backface Tip clearance Volute Geometry Spreadsheet based design Mass + angular momentum conservation approach (free vortex) Drives a parameterized DesignModeler geometry

38 Compressor Design Requirements Parameter Value Diameter 48 [mm] Number of Vanes Inlet Temperature 288 [K] Inlet Pressure [kpa] Mass Flow Rate 0.12 [kg/s] Pressure Ratio 2.15 Tip Speed 391 [m/s] High Specific Flow impeller with vaneless diffuser of radius ratio 1.7 Typical for a gasoline engine with capacity of 1.6L. Mid map operating point Shaft Speed 155,733 [rev min^ 1]

39 Initial Sizing Vista CCD used to create a geometry from design requirements

40 Vista CCD: Output Iterate in CCD to achieve acceptable preliminary design

41 Vista CCM: Input Vista CCM used to create a preliminary compressor map

42 Vista CCM: Output Turbocharger compressor is typically operating at off design

43 Initial Geometry Creation VISTA TF requires a geometry: from BladeModeler Push button solution from Vista CCD Compressor Shroud Section

44 Initial Geometry Creation Compressor Hub Section

45 Vista TF: 2D Analysis Vista TF is a throughflow (streamline curvature) solver Used to provide further insight into design Contour plots show circumferentially averaged quantities 2D Charts show various design parameters such as loading, incidence and deviation Based on results, geometry can be quickly modified and analyzed again Blade and flowpath design improved Can be parametric and optimization can be performed

46 Vista TF: Qualitative Output Tangential velocity Solution error Meridional velocity Static pressure

47 Vista TF

48 Final Impeller Design Final impeller geometry steps prior to meshing Direct to TurboGrid for hex Create fluid flow path for tet meshing Volute geometry is generated to match impeller Details later

49 Final Geometries Impeller and vaneless diffuser Volute

50 Meshing Impeller Mesh Use a hexahedral mesh: TurboGrid ATM Pay attention to: Target mesh size Balance Boundary layer resolution Y+ Tip clearance Aspect ratio Volute mesh ANSYS meshing Tets + prisms for boundary layer resolution Local mesh refinement near tongue Match diffuser outlet/volute inlet spanwise mesh distribution

51 Impeller only Analysis Impeller + part of vaneless diffuser How much of the vaneless space to model? Grid refinement study Grid: The biggest factor affecting predictions Tetrahedral Elements Vs. Hexahedral Elements Understand the effect of grid size on prediction Target: working grid size with Y+=2 Ideally, double/half the grid size in each direction 1/8X, 1X, 8X working grid size Estimate of grid independent solution Effect of fillets Look at key points on the map Nominal design, near surge line, near choke, choke

52 Example: Mesh Independence Study Impeller + Vaneless Diffuser Analyzed at 155, 733 rpm Three operating points Design Flow Rate Near Choke Near Stall/Surge Compared Hex mesh vs. Tet mesh

53 Mesh Summary Hexahedral #of Nodes Blade Y+ Meshing Tool Meshing Method Meshing Time Mesh File Size Max Vol Ratio Max Length Ratio 0.142m 8 TurboGrid ATM 1 min 3.67MB m 4 TurboGrid ATM 1 min 34.8MB m 2 TurboGrid ATM 3 min 273MB Tetrahedral #of Nodes Blade Y+ Meshing Tool Meshing Method Meshing Time Mesh File Size Min Angle Min Quality 0.143m 8 ICEM CFD Octree ~5 min 56.7MB m 4 ICEM CFD Octree ~30 min 601MB m 2 ICEM CFD Octree ~1.5 hr 4.4GB e 06

54 Hex Coarse Mesh

55 Hex Medium Mesh

56 Hex Fine Mesh

57 Tet Coarse Mesh

58 Tet Medium Mesh

59 Tet Fine Mesh

60 Mesh Independence: Hex vs. Tet Total Pressure Tet mesh at approximately 8 million nodes still is not as accurate as Hex mesh at 125 thousand nodes!

61 Mesh Independence: Hex vs. Tet Isentropic Efficiency

62 Mesh Sensitivity: Hex speedline

63 Mesh Sensitivity: Fine Tet speedline added Tet mesh at approximately 8 million nodes still is not as accurate as Hex mesh at 125 thousand nodes!

64 Effect of Fillet 1.5 mm fillet included at main and splitter blade root compared to blade geometry without fillet

65 Fillet Study: Effect on Pressure Ratio Difference only apparent at/near choke

66 Fillet Study: Effect on Isentropic Efficiency Difference only apparent at/near choke

67 Assembly Analysis How much do I really need to model, and using what methods? Impeller diffuser volute? Volute only (including part of vaneless diffuser)? Inlet specified from exit of impeller only analysis Steady state, transient? We did the following, for comparison purposes: Frozen rotor full 360 degrees Stage analysis one impeller with full volute Transient Rotor Stator full 360 degrees Volute only Constant Pt, Tt, flow direction As above but with a spanwise profile

68 Volute Mesh Relatively Coarse Mesh used for Study Size: 370,000 nodes Tet Elements = 1.1 million Prism Elements = 0.32 million Quality Statistics Average Element Quality = 0.71 Min Element Quality = 0.046

69 Effects of Diffuser and Volute Comparison of three different configurations Impeller Only (Single Passage) Impeller + Vaneless Diffuser (Single Passage) Impeller + Vaneless Diffuser + Volute (Full 360, frozen rotor) Compare speedlines 155,733 rpm Pt ratio = (Pt outlet/pt inlet) Isentropic Efficiency

70 Pressure ratio predictions

71 Isentropic efficiency predictions

72 Impeller Behavior Now look at impeller only performance in two configurations Impeller only simulation Impeller diffuser volute simulation Speedlines shows Impeller behaves similarly regardless of downstream geometry Pt ratio = (Pt impeller outlet/pt impeller inlet) Isentropic Efficiency for impeller only Significant value in examining individual components to gain insight

73 Impeller pressure ratio predictions for two configurations

74 Isentropic efficiency predictions for two configurations

75 Effect of rotating stationary frame interface type Comparison of three interface types between diffuser and volute Stage (single passage impeller/diffuser, full volute) Frozen rotor (full 360 degrees) Transient Rotor Stator For all cases Impeller + vaneless diffuser modeled in rotating frame Volute modeled in stationary frame

76 Effect of interface type on total pressure prediction

77 Effect of interface type on isentropic efficiency prediction

78 Post Processing Before starting: Make sure solutions are converged! Run with a big enough time step! Quantitative Impeller Pt, Tt, Abs. flow angle, isentropic efficiency Distortion factor Blade loading Volute: recovery factor, loss coefficient Estimate grid independent solution Qualitative Blade to blade and meridional averaged Unrolled plot at exit of impeller

79 CFD Results Examine results from Compressor Report in CFD Post

80 CFD Results Or use table generation tool in CFD Post to extract custom information at various streamwise locations

81 Blade Loading Chart near choke Mass flow = 0.13 kg/s

82 Relative Mach Number near choke Mass flow = 0.13 kg/s

83 Relative Velocity near choke Mass flow = 0.13 kg/s

84 Meridional velocity near choke Mass Flow = 0.13 kg/s

85 Static pressure near choke Mass flow = 0.13 kg/s

86 Relative Mach Number near choke Mass flow = 0.13 kg/s

87 Summary ANSYS offers complete turbomachinery design and analysis software Geometry Throughflow Meshing CFD Thermal Combustion Structural mechanics Rotordynamics Post processing Optimization